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A strong electric field can be generated when the shock‐induced depoling current from a normally poled PZT 95/5 sample is passed through a large resistive load. The portion of total depoling current that is retained on the sample electrodes to account for capacitance is governed by the dynamic dielectric properties of both unshocked and shocked material. Early studies used measured load currents from single samples to assess models for dielectric response. In more recent studies, we used shock‐driven circuits in which multiple PZT 95/5 elements were displaced both parallel and perpendicular to the shock motion. This allowed both load and charging currents to be measured for individual elements that are subjected to shock compression and release at different times. In the present study, these techniques have been utilized to examine dielectric properties in PZT 95/5 samples at initial temperatures from −56 to 74 °C. Significant changes in permittivity with temperature are observed in both unshocked and sho...

Alumina‐filled epoxies are composites having constituents with highly dissimilar mechanical properties, resulting in complex behavior during shock compression and release. Two distinguishing characteristics are amplitude‐dependent wave structures and high release wave velocities. Recent studies examined the effects of various compositional changes on these shock properties. As expected, the strongest effects were observed when the total alumina volume fraction was reduced in steps from a nominal 43% to 0%. In the present study, compositions prepared over the same range of alumina loadings were examined at initial temperatures that were nominally −55 °C or 70 °C. Experimental configurations were identical to previous room‐temperature experiments. Laser interferometry and wave timing were used to obtain transmitted wave profiles, Hugoniot states, and release wave velocities. Initial densities were determined from thermal expansion coefficients measured for each composition. Although initial density changes ...

Shock‐induced depoling of the ferroelectric ceramic PZT 95/5 is utilized in pulsed power devices. High electric fields are generated within a normally poled ceramic element when the depoling current is passed through a large load resistor. Under these conditions, a portion of the depoling current is retained on the element electrodes to account for capacitance. This effect is governed by the dielectric properties of both unshocked and shocked PZT 95/5 as the field develops during shock transit. Previous studies proposed either constant or relatively simple relaxing behavior for dielectric properties on either side of the shock front. However, interpretation of the corresponding experiments was complicated by possible field effects on depoling kinetics. Recent studies have used different experimental configurations to better isolate the dielectric behavior. Multiple PZT 95/5 elements are displaced both parallel and perpendicular to the direction of shock motion to allow for sequential charging of unshocked and shocked samples. These experiments show a dielectric behavior for which a simple relaxation model is inadequate.

Alumina‐filled epoxies are used to encapsulate ferroelectric ceramics in shock‐driven, pulsed power devices. Device performance is strongly influenced by the shock compression and release properties of the encapsulant, which must be adequately understood in order to develop a capability for numerically simulating the operation of these power sources. In previous studies, Hugoniot states and release velocities were measured in reverse‐impact experiments using laser interferometry (VISAR) at stresses up to 5 GPa. In addition, wave profiles were obtained in transmitted‐wave experiments at fixed impact conditions as a function of initial temperature. These experiments showed an extended wave structure having a rise time that increased with decreasing temperature. In recent studies, Hugoniot states and release velocities at stresses up to 10 GPa have been obtained in reverse‐impact experiments. Transmitted‐wave experiments have examined the effects of wave amplitude on the wave structure and also the evolution...

The shock and release behaviors of both alumina‐filled and unfilled epoxies are examined in planar impact experiments over an initial temperature range of −50 to +70 C. The materials under investigation can be used as encapsulants in applications such as shock‐activated pulsed power supplies. Characterizing the effect of initial temperature on their dynamic behavior under shock loading and subsequent release is part of a larger effort to develop predictive numerical models for the performance of these power sources. In the current study, transmitted waveforms were recorded using laser interferometry (VISAR) to examine initial temperature effects on the inelastic behavior in these materials. Current results, combined with the results of previous studies of these epoxies at ambient temperature, show a clear trend of increasing inelastic features in compressive waveforms with decreasing temperature. Temperature effects are more pronounced in the filled samples. In both cases, release wave speeds decrease wit...

The shock and release behavior of both alumina-filled and unfilled epoxies are examined in planar impact experiments. The various materials investigated can be used as encapsulants in applications such as shock-activated pulsed power supplies. Characterizing their dynamic behavior under shock loading and subsequent release is part of a larger effort to develop predictive numerical models for the performance of these power sources. In the current study, reverse-impact techniques were used to establish Hugoniot states and subsequent release profiles for each material at several impact conditions. Laser interferometry (VISAR) was used in these experiments to determine the particle velocity history at the impact interface formed by a projectile-mounted epoxy sample and a stationary fused silica target. Conventional impact configurations and VISAR were used to observe transmitted waveforms under corresponding shock loading conditions. Transmitted waveforms at multiple Lagrangian locations were also recorded in selected experiments using embedded PVDF piezoelectric films. The results show expected differences in the dynamic properties of filled and unfilled epoxies, and similarities in the properties between different filled or unfilled epoxies. Comparisons between VISAR experiments and PVDF gauge experiments may indicate a rate-dependent response in this gauge material.

Shock-induced depoling of the ferroelectric ceramic PZT 95/5 is utilized in a number of pulsed power devices. Several experimental and theoretical efforts are in progress in order to improve numerical simulations of these devices. In this study we have examined the shock response of normally poled PZT 95/5 under uniaxial strain conditions. On each experiment the current produced in an external circuit and the transmitted waveform at a window interface were recorded. The peak electrical field generated within the PZT sample was varied through the choice of external circuit resistance. Shock pressures were varied from 0.6 to 4.6 GPa, and peak electrical fields were varied from 0.2 to 37 kV/cm. For a 2.4 GPa shock and the lowest peak field, a nearly constant current governed simply by the remanent polarization and the shock velocity was recorded. Both decreasing the shock pressure and increasing the electrical field resulted in reduced current generation, indicating a retardation of the depoling kinetics.

Shock-induced depoling of the ferroelectric ceramic PZT 95/5 has been utilized in pulsed power applications for many years. Recently, new design and certification requirements have generated a strong interest in numerically simulating the operation of pulsed power devices. Because of a scarcity of relevant experimental data obtained within the past twenty years, we have initiated an extensive experimental study of the dynamic behavior of this material in support of simulation efforts. The experiments performed to date have been limited to examining the behavior of unpoled material. Samples of PZT 95/5 have been shocked to axial stresses from 0.5 to 5.0 GPa in planar impact experiments. Impact face conditions have been recorded using PVDF stress gauges, and transmitted wave profiles have been recorded either at window interfaces or at a free surface using laser interferometry (VISAR). The results significantly extend the stresses examined in prior studies of unpoled material, and ensure that a comprehensive experimental characterization of the mechanical behavior under shock loading is available for continuing development of PZT 95/5 material models.

Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties, resulting in complex behavior during shock compression and release. A previous study examined the shock properties of a particular composition in some detail. In the current study, the effects of compositional variations on shock properties were examined. Planar-impact experiments producing states of nearly equal strain were conducted to investigate the effects of changes in the size and shape of alumina particles, and in the total volume fraction of alumina. Laser interferometry and wave timing were used to obtain transmitted wave profiles, Hugoniot states, and release wave velocities. In addition, wave profiles and velocities were obtained in “thin-pulse” experiments that examined the combined effects of compression and release properties in different compositions. Changes in the size and shape of alumina particles were found to have little effect except in the viscous spreading of wave profiles durin...

Alumina-filled epoxies are composites having constituents with highly dissimilar mechanical properties. Complex behavior during shock compression and release can result, particularly at higher alumina loadings. In the current study, a particular material containing 43% alumina by volume was examined in planar-impact experiments. Laser interferometry was used to measure particle velocity histories in both reverse-impact and transmitted-wave configurations. Hugoniot states and release-wave velocities were obtained at shock stresses up to 10GPa, and represented smooth extensions of previous data at lower stresses. Surprisingly high release-wave velocities continued to be the most notable feature. Measured profiles of transmitted waves show a gradual transition from viscoelastic behavior at high shock stresses to a more complex behavior at lower stresses in which viscous mechanisms produce a broadened wave structure. This wave structure was examined in some detail for peak stress dependence, evolution towards...

Raman spectroscopy has the potential of providing detailed temperature and composition measurements at discrete points within a mixture of gases. Although cross sections for Raman scattering are characteristically very small, recent developments in high power lasers and sensitive optical detectors have resulted in the application of Raman spectroscopy to a variety of new experimental studies. Current applications include the remote measurement of atmospheric constituents and temperatures, concentration measurements in heterogeneous, nonreacting gasdynamic processes, remote detection of pollutants in gas turbine exhaust, and temperature and composition measurements in steady flame gases.

We developed a convenient laboratory procedure to determine forces on projectiles penetrating geological targets. Gas guns were used to accelerate foundry core targets (a simulated soft sandstone) to steady velocities, and the targets subsequently impacted 20.6-mm-dia penetrators instrumented with piezoelectric accelerometers. Rigid-body acceleration data were recorded for one ogival and two conical nose shapes for impact velocities between 0.2-1.2 km/s.

Spectral interferences to Raman bands due to laser-induced fluorescence are examined in exhaust gases from an internal combustion engine operating on different fuels and fuel/air mixtures. A broadband fluorescence spectrum is observed in all cases, but the relative fluorescence intensity depends strongly on the particular engine operating condition. Elimination of the fluorescence background by various exhaust conditioning devices confirmed the fact that aerosols of hydrocarbons or other organic compounds are the principal source.

For nearly twenty years the Sandia 25‐meter compressed gas gun has been an important tool for studying condensed materials subjected to transient shock compression. Major system modifications are now in progress to provide new control, instrumentation, and data acquisition capabilities. These features will ensure that the facility can continue as an effective means of investigating a variety of physical and chemical processes in shock‐compressed solids.

Hexanitrostilbene (HNS) is a binderless, granular explosive prepared over wide ranges of initial grain size and final bulk density. During shock initiation of HNS, ignition initially occurs at discrete hot spots formed during the dynamic compaction of the porous material. In order to develop a predictive understanding of the shock initiation mechanisms occurring in this explosive, it is necessary to formulate constitutive relations modeling the mechanical response of HNS materials under compressive loading. In an early study of HNS properties, Sheffield et al. [1] established shock Hugoniot properties and formulated an equation of state for bulk densities of 1.0 – 1.7 g/cc (crystal density is 1.74 g/cc). Subsequently, Hayes and Mitchell [2] and Hayes [3] developed a model for the shock compaction and chemical decomposition of HNS. In these studies, the non-reactive material response was treated as depending only on the initial bulk density (related to initial porosity) of the HNS sample. Our recent studies [4,5] have established that the shock sensitivity of HNS samples pressed to a common density depends critically on the initial grain size distribution of the material. In the present study, we have undertaken both experimental and analytical studies of the compressibility behavior of HNS under non-reactive conditions.

Raman spectroscopy is evaluated as a method for analyzing mixtures of hydrogen isotopes, Raman vibrational spectra of the various diatomic isotopes are described, and an existing Raman analysis system is evaluated for sensitivity. An optimized analysis system utilizing an intra-cavity optical cell is described, and its potential sensitivity evaluated. Raman techniques are shown to be capable of accurate concentration measurements with excellent resolution of the diatomic isotopes.